The new added files don't have copyright declaration

[WillemJiang]

Describe the bug (描述bug)
I just made some comparison by using python script， I found the initial commit has some newly added source files as below

src/brpc/span.cpp
src/brpc/streaming_rpc_meta.proto
src/bthread/bthread_cxx.cpp
src/bthread/bthread_cxx.h
src/bthread/mtx_cv_base.h
src/bvar/detail/histogram.cpp
src/bvar/detail/histogram.h
src/bvar/latency_histogram_recorder.cpp
src/bvar/latency_histogram_recorder.h
src/sanitizer/tsan_interface_atomic.h

These files do have the copyright declaration as Apache License suggested like this.

   Copyright [yyyy] [name of copyright owner]

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.

[WillemJiang]

Some newly added files already have the license header, which means they may copy from other projects.
Please only change the license header by adding the copyright declaration in those files if you made significant changes there.